1. Field of the Invention
The present invention relates to a novel norbornane type ester hydrolase that enantio-selectively hydrolyzes a (.+-.)-exo-norbornane type ester to produce optically active norborneol; a structural gene of the norbornane type ester hydrolase; an expression vector including the structural gene; a transformant including the expression vector; and a production method for the norbornane type ester hydrolase using the transformant.
2. Description of the Related Art
Several methods for preparing norborneol are known in the art. The known methods are classified into chemical and biological methods. For example, the following chemical method is known. Norbornene used as a starting material is allowed to react with an organic acid to produce a norbornane type ester compound. The ester compound is chemically hydrolyzed to produce norborneol. In this chemical method, four kinds of stereoisomers of norborneol (i.e., (+)-endo-norborneol, (-)-endo-norborneol, (+)-exo-norborneol and (-)-exo-norborneol) are simultaneously produced. Therefore, a complicated separation is further required to obtain an optically active norborneol.
Another production method for norborneol using the following biological method is also known. Norbornene used as a starting material is allowed to react with an organic acid to produce a norbornane type ester compound. The ester compound is allowed to react with an enzyme, or to come in contact with microorganisms producing such an enzyme, thereby hydrolyzing the ester compound to obtain norborneol. With regard to this biological method, Oberhauser et al. reported a method for producing (-)-norborneol from (.+-.)-norbornyl acetate by using a lipase derived from Candida cylindraceae (Th. Oberhauser et al., Tetrahedron, 43, 3931-3941, 1987). The method using the lipase, however, has a low selectivity and the produced norborneol has a low optical purity.
Japanese Laid-Open Patent Publication No. 2-273196 discloses an optical resolution method of a racemic mixture using a biological hydrolysis reaction, in which an inhibitor for selectively inhibiting the hydrolysis reaction of one of the enantiomers is used in the reaction. Such a method can be employed to prepare optically active norborneol. In this method, however, it is necessary to perform a screening of inhibitors to obtain an inhibitor that is useful in the selection of the optically active norborneol. Further, it is required to remove the inhibitor after the reaction. As a result, such a method is disadvantageously complicated.